The research objective of this proposed study is to examine the relative contribution of sinoaortic baroreceptors in controlling changes in renal function during alterations in effective circulating blood volume. Studies will be conducted in control dogs and dogs with selectively denervated sinoaortic baroreceptors to determine if the reflex antidiuresis associated with the application of positive end expiratory pressure breathing and the reflex diuresis of atrial tachycardia are initiated by sinoaortic baroreceptors. Also, the role of sinoaortic baroreceptors and cardiopulmonary receptors in influencing renal function in response to a hemorrhage of 10% will be examined.